The invention relates to a method and apparatus for anchoring an optical fiber.
FIG. 6 is a cross-sectional view of an example of an optical submarine cable.
The optical submarine cable shown in the drawing comprises: an optical core 1; steel wires 2 provided around the optical core 1; a copper tube 3 provided on the periphery of the steel wires 2; a waterproofing compound 4 provided among the optical core 1, the steel wires 2, and the copper tube 3; and an insulator 5 provided as the outermost layer.
FIG. 7 is a cross-sectional view of an example of the conventional optical core used in the optical submarine cable shown in FIG. 6.
The optical core 1 for an optical submarine cable shown in FIG. 7 comprises: a central tension member 6; a plurality of optical fibers 7 disposed parallel to the central tension member 6 or spirally around the central tension member 6; and a plastic filler 8 filled into gaps between the central tension member 6 and the optical fiber 7 so as to have a circular section.
In anchoring this type of optical submarine cable to a predetermined position, the central tension member 6 of the optical core 1 has hitherto been mechanically fixed onto the predetermined position (coupling with a joint and a repeater not shown).
On the other hand, in order to cope with wavelength multiplexing in an optical transmission system, optical fibers of large mode and low dispersion or low dispersion slope, which are different from the conventional optical fiber, have come into use. Since these optical fibers have a complicate profile, the conventional optical core structure has been likely to increase transmission loss.
A loose tube-type optical core structure as shown in FIG. 8, which is less likely to increase the transmission loss, has become adopted as a measure for reducing the transmission loss.
FIG. 8 is a cross-sectional view of another example of the conventional optical core used in the optical submarine cable shown in FIG. 6.
The optical core 9 shown in FIG. 8 comprises: parallelly or spirally disposed optical fibers 7; a jelly 10 filled around the optical fibers 7 so as to have a circular section; and a plastic tube 11 provided on the periphery of the jelly 10.
Unlike the optical core 1 shown in FIG. 7, the loose tube-type optical core 9 shown in FIG. 8 does not have a central tension member 6, and thus makes it necessary to directly anchor the optical fibers 7.
FIG. 9A is a plan and perspective view of an apparatus to which a conventional optical fiber-anchoring method has been applied. FIG. 9B is a cross-sectional view taken on line Axe2x80x94A of FIG. 9A.
In this apparatus, the anchor position of a plurality of optical fibers 12 is formed in a tape form using an adhesive 13. The optical fibers 12 in their tape portion is inserted into a through hole in a shrinkable tube 15 containing two shrinkable tube reinforcements 14, followed by heating for integration. The shrinkable tube 15 is then placed within a shrinkable tube fixing material 16 which is then fixed to anchor the optical fibers 12. Numeral 17 designates an adhesive applied to the inside of the through hole in the shrinkable tube 15.
In this method, it is considered that the shrinkable tube 15 applies a lateral pressure, the adhesive 17 enhances the coefficient of friction, and, in addition, the adhesive force of the adhesive 17 is utilized. The magnitude and direction of anchor force P or the like in the anchoring apparatus are shown in FIG. 10 and are expressed by the following equation;
F=xcexcWL+F0
wherein F: anchor force, N;
xcexc: coefficient of friction;
W: lateral pressure by the shrinkable tube, N/m;
L: length which receives lateral pressure, m; and
F0: adhesive force of the adhesive, N.
FIG. 10 is a conceptual view illustrating the anchor force applied to the optical fiber in the anchoring apparatus.
The prior art techniques described above, however, had the following problems.
(1) For the method wherein a lateral pressure is applied to optical fibers to anchor the optical fibers, the lateral pressure is likely to increase the transmission loss.
(2) The anchor force depends upon the coefficient of friction between the fixing material and the optical fibers. Since, however, one of the two members is the optical fiber, it is difficult to provide a large coefficient of friction. Even when an adhesive is applied to enhance the coefficient of friction, good long-term reliability cannot be realized without difficulty.
(3) It is difficult to realize good long-term reliability in terms of the adhesive force of the adhesive.
Accordingly, it is an object of the invention to solve the above problems of the prior art and to provide an optical fiber-anchoring method and an optical fiber-anchoring apparatus which can realize no significant transmission 1088 of the optical fiber, good long-term reliability, and satisfactory anchor force.
In order to attain the above object, according to the first feature of the invention, an optical fiber-anchoring method comprises the steps of:
fixing a covering material onto the anchor position of at least one optical fiber so as to cover the anchor position, said covering material having been produced from substantially the same material as a jacket material of the optical fiber;
fixing the covering material to the inside of a fixing material for anchoring; and
anchoring the fixing material to a predetermined position.
According to the second feature of the invention, an optical fiber-anchoring method comprises the steps of:
fixing a covering material onto the anchor position of a tension member and at least one optical fiber so as to cover the anchor position, said covering material having been produced from substantially the same material as a jacket material of the optical fiber; and
anchoring the tension member.
According to the third feature of the invention, an optical fiber-anchoring apparatus for anchoring at least one optical fiber, comprises:
a covering material fixed onto the anchor position of the optical fiber so as to cover the anchor position, said covering material having been produced from substantially the same material as a jacket material of the optical fiber; and
a fixing material to which the covering material is fixed and which is anchored to a predetermined position.
According to the optical fiber-anchoring apparatus of the invention, in addition to the above construction, the covering material preferably has a convex and the fixing material has a concave into which the convex is fitted.
According to the fourth feature of the invention, an optical fiber-anchoring apparatus for anchoring at least one optical fiber, comprises:
a tension member arranged in combination with the optical fiber; and
a covering material fixed onto the anchor position of the tension member and the optical fiber so as to cover the anchor position, said covering material having been produced from substantially the same material as a jacket material of the optical fiber.
According to the optical fiber-anchoring apparatus of the invention, in addition to the above construction, the covering material preferably has been produced from a UV-curable resin.
Substantially the same material as a jacket material of an optical fiber, for example, a UV-curable resin, is molded into a shape which covers the anchor position of an optical fiber and has in its center a convex for facilitating anchoring. Ultraviolet light is then applied to cure the UV-curable resin to form a covering material. Since this covering material is substantially the same as the jacket material of the optical fiber, the adhesive strength between the optical fiber and the covering material is high. Further, there is no chemical adverse effect on the optical fiber to provide good long-term reliability.
On the other hand, the fixing material is not anchored to the covering material by the lateral pressure, but by a method wherein a groove for receiving the covering material is provided inside the fixing material so that the convex of the covering material is fitted into the groove to apply a stress to the shearing direction, whereby the tensile stress of the optical fiber becomes the shearing force of the covering material in its convex. As a result, the optical fibers can be anchored without substantially increasing the transmission loss.